1. Field of the Invention
The present invention relates to a process for forming a fine resist pattern and more particularly to a novel and simple process for forming a fine resist pattern in a photolithographic technology.
2. Description of Related Art
The recent advancement in a semiconductor device manufacturing technology has given rise to a demand for a photolithographic technology for forming a superfine pattern in the order of 0.5 .mu.m. As to a technology for forming a superfine pattern in the order of 0.5 .mu.m or even smaller, in the aspect of apparatus, there have been made the studies of techniques for shortening the wavelength of the conventional stepper and widening the numerical aperture thereof. Besides, as new apparatuses for forming superfine patterns, there are being developed an excimer laser stepper, an X-ray stepper and a direct writing type electron beam exposure apparatus.
There is, however, a definite limit to the widening of numerical aperture and the shortening of wavelength of the conventional stepper; the fabrication of a mask for an X-ray stepper is difficult and a throughput is low in a direct writing type electron beam exposure apparatus. Because of these reasons, an excimer laser stepper is presently considered to be the most hopeful one. The excimer laser stepper, however, has its own demerits. That is, as expressed in the following Reyleigh's equation (1): EQU R=k.lambda./NA (1)
wherein R is a resolution, k is a constant (from 0.6 to 0.8), .lambda. is an exposure wavelength and NA is a numerical aperture of lens, the value of NA must be increased in order to improve the resolution without changing the wavelength of a stepper, but a focal depth (FD) becomes shallower as shown in the following equation (2): EQU FD=.lambda./(NA).sup.2 ( 2)
when the value of NA is increased.
On the other hand, various methods have been proposed and attempted in a resist process technology, too. For example, there are known a multilayer resist method (MLR method), an antireflective coating method (ARC method), a contrast enhanced lithography method (CEL method), a portable conformable mask method (PCM method), an image reversal method (IR method) and the like. Although these methods are effective to compensate for the shallow focal depth in the photolithographic technology, they are not very practical because their processes are complicated or because the effect of increasing focal depth is not sufficient.
Therefore, the conventional resist process technology is not enough to cope with the shallow focal depth accompanied by the shortening of wavelength and the widening of numerical aperture in an excimer laser stepper.
Also, the present inventor has proposed in U.S. application Ser. No. 159,294 a process for forming a pattern which comprises forming an exposed layer by selectively irradiating the surface of an applied resist with a first energy beam; allowing a substance (dyestuff) which absorbs a second energy beam to adhere to the exposed layer; exposing the whole surface of the applied resist with the second energy beam and removing the portion of the resist where the exposed layer is not formed, by developing the resist. Hereinafter, this process is referred to as a Dye Image Reversal method (DIR method).
In the above-mentioned U.S. application Ser. No. 159,294, for example, there is disclosed the example using a resist comprising a novolak-type resin and a naphthoquinone diazide-type photosensitizer. Since, however, the naphthoquinone diazide-type photosensitizer is converted into indene carboxylic acid by the exposure with the first energy beam in a novolak-type resin, the converted photosensitizer is eluted and hence the surface of the applied resist becomes rough when the exposed layer is dyed by an alkaline dyestuff. The roughness of the surface is a disadvantage of forming a fine resist pattern.